Controlling Nucleation and Crystal Growth Orientation via Intermediate Ion-Complex Formation for Efficient α-FA0.95Cs0.05PbI3 Perovskite Solar Cells

摘要

The formamidinium–cesium (FA–Cs) alloyed metal halide perovskites demonstrate superior photovoltaics device stability; however, alloying at lower Cs concentrations (≤5) undergoes complex intermediate phase transitions that disrupt morphological and structural properties. Herein, an intermediate ioncomplex method in a bid is attempted to achieve a near-optimal energy bandgap of 1.52 eV for α-FAPbI3 perovskite (alloyed with 5 Cst cation). Upon incorporation of judicious amount of smaller and more volatile ions (such as Cl/Br and methylammonium MAt/Cst) into the host FAPbI3 system, these ions are observed to persist in the “transitional-phase” and “stimulate” the formation of α-phase. Consequently, using X-ray and photoluminescence quantum efficiency measurements, the formation of a (110)-plane-oriented high-quality FA0.95Cs0.05PbI3 perovskite thin film with significantly reduced nonradiative recombination is confirmed. An area of 25mm2 yields a power conversion efficiency (PCE) of 20.21 and a stabilized power output of 19.82, leveraging open-circuit voltage of 90.4 of that Shockley–Queisser limit. The devices sustain over 1000 h without any PCE degradation.